Nelson T E
Biochim Biophys Acta. 1975 Jan 23;377(1):139-45. doi: 10.1016/0005-2744(75)90294-6.
The attack mechanism of a purified exo-1,3-beta glucosidase (1,3-beta-D-glucan glucohydrolase, EC 3.2.1.58) was investigated by using as a substrate a mixture of two structurally characterized periodate-oxidized and reduced unbranched 1,3-beta-D-glucans which differed only at the reducing terminal. The substrates, derivatives of laminarin, were altered only at the terminals due to resistance of the internal (1 leads to 3)-linked glucosyl residues to periodate oxidation. Each glucan has only a single and identical altered non-reducing terminal per molecule. Upon enzymatic hydrolysis, one molar equivalent of glycerol was produced from the altered non-reducing terminal of each substrate molecule attacked. Using glycerol as an indication of the number of chains acted upon, the quantity of D-glucose produced from the internal residues was used to determine the extent to which a chain was initially attacked. The glucose to glycerol ratio during the course of the hydrolysis indicates that the enzyme proceeds by a multiple-attack mechanism where four glucosyl residues are successively removed per encounter from the non-reducing terminal of each substrate molecule.
通过使用两种结构特征明确的高碘酸盐氧化和还原的无分支1,3-β-D-葡聚糖的混合物作为底物，研究了纯化的外切1,3-β-葡糖苷酶（1,3-β-D-葡聚糖葡糖水解酶，EC 3.2.1.58）的攻击机制，这两种葡聚糖仅在还原末端有所不同。底物海带多糖的衍生物仅在末端发生改变，这是由于内部（1→3）连接的葡糖基残基对高碘酸盐氧化具有抗性。每个葡聚糖分子每分子仅具有一个且相同的改变的非还原末端。在酶促水解时，每个被攻击的底物分子的改变的非还原末端产生一摩尔当量的甘油。使用甘油作为作用链数的指示，由内部残基产生的D-葡萄糖量用于确定链最初被攻击的程度。水解过程中的葡萄糖与甘油比率表明，该酶通过多重攻击机制进行，每次从每个底物分子的非还原末端连续去除四个葡糖基残基。
